Refrigerator Problem: Testing Compressor with 2 Wires & 3 Terminals

[zoobyshoe]

My refrigerator stopped working. I found that the relay switch that activates the compressor is cripsy fried.

I called a local appliance parts store and it looks like I can buy a replacement for the switch. However, I am wondering why it fried in the first place. I want to test the compressor but I don't understand the hookup. Two wires go into the relay, but the relay attaches to the compressor with three terminals.

Can I test the compressor by touching the two wires to two of the three terminals? If so, which two?

Thanks.

 

[NeuronsAtWork]

I would not recommend trying to manually run the compressor in the way you suggest. The relay is a start relay; it briefly applies voltage to both the start and run windings of the compressor then opens and places the run capacitor in the circuit after the unit starts. It usually also contains an overload switch to cut power if the compressor locks up. Odds are it just wore out, or a contact was loose and that built up heat which fried the relay. Make sure the compressor contacts are clean and do not show signs of arcing. The relay should be pretty cheap, and I doubt there's anything wrong with the compressor. One thing to remember--if the compressor is running, then the power is cut for whatever reason, the compressor needs to sit for 10 minutes or so so pressures can equalize before restarting it--otherwise it will lock up for a time and trip the overload every minute or so until it can start. This is hard on it, and should be avoided.

 

[zoobyshoe]

I would not recommend trying to manually run the compressor in the way you suggest. The relay is a start relay; it briefly applies voltage to both the start and run windings of the compressor then opens and places the run capacitor in the circuit after the unit starts. It usually also contains an overload switch to cut power if the compressor locks up. Odds are it just wore out, or a contact was loose and that built up heat which fried the relay. Make sure the compressor contacts are clean and do not show signs of arcing. The relay should be pretty cheap, and I doubt there's anything wrong with the compressor. One thing to remember--if the compressor is running, then the power is cut for whatever reason, the compressor needs to sit for 10 minutes or so so pressures can equalize before restarting it--otherwise it will lock up for a time and trip the overload every minute or so until it can start. This is hard on it, and should be avoided.

Thanks very much!

The compressor contacts are not clean. On one of them metal from the inside of the relay was outright welded to the pin.

I checked across the pins with an ohm meter set at RX1. Two combinations gave me about 7 ohms and the other about 11 ohms. The didn't seem to be any shorts to the compressor housing, though. I scraped paint off, put one lead from the meter on the bare spot and touched the other lead to the three pins in succession. No continuity. The ohms seem high by the two sites I found though. One said they should all register zero ohms. A youtube video declared a compressor good at around 2 ohms. I'm not sure if 7-7-11 is just too high or not.

The relay plus cap was quoted to me at about $50. That's not cheap enough to fry just in order to discover the compressor is bad.

Thanks again for the thorough answer.

 

[NeuronsAtWork]

Well, I see your point. Those ohm readings do sound somewhat high, but I have nothing here with which to compare them. As long as you aren't getting a direct short or an open odds are you are okay, though. The three contacts on the compressor (as you likely know) are S (start), R (run), and C (common). One winding goes from S to C and the other from R to C. And based on what you said there is no short to ground, which is a good thing. It just sounds like one push on contact got loose and arced. This is concerning, because if the pin is damaged to that extent it becomes difficult to ensure that the new relay with make consistent contact in the future. I'm not sure what to tell you as the correct course of action. That price is higher than I remember or would have thought, so perhaps check around or online with Amazon or the like. If it looks like you can lightly sand the pin to get it back to shiny and shaped right you might be able to feel safe just replacing the relay. If not...? Not sure as replacing the compressor would likely cost more than another (perhaps used) fridge. Maybe soldering leads to the comp. and mounting the relay a short distance away? I'm at a loss...

 

[jim hardy]

a google search on the model number of the appliance will usually take you to a wiring diagram. Maybe armed with that you can identify run start and common terminals... the "start capacitor" is a part notorious for lasting not so long as rest of the fridge... should cost less than $10 in US

A google search on the model number of the compressor will usually take you to a manufacturer's datasheet for the compressor. Appliance manufacturers tend to buy compressors from a third party rather than make their own. Most i run across are either Copeland or Matsugarbagea. The datasheet should tell you what is winding resistance. A small 240 volt model will be more ohms than a big 120 volt one.

soldering leads to compressor sounds viable. Just be sure that your relay isn't one of those with a thermal probe inserted in a well inside the compressor, that style needs to be aware of motor temperature to protect the windings.

 

[zoobyshoe]

Thank you both very much! I think I have plenty of information to proceed.

This is really my landlady's problem, but to the extent I can avoid her having to but me a new fridge she's less likely to think about raising my rent, you see. (She's already had to buy me a new stove when the old one started leaking gas. It wasn't a cheap fix.)

I very much appreciate both your responses!